Check column existence
Using cqlsh, you can either get the description of all columns and their data types, or discover whether a particular column exists in a table by querying the column’s data.
All columns
The CQLSH command DESCRIBE TABLE shows all the table information, including the columns defined.
For example, if the cycling.comments table is defined, the following will return the table definition:
DESCRIBE TABLE cycling.comments;Results
CREATE TABLE cycling.comments (
id uuid,
created_at timestamp,
comment text,
commenter text,
record_id timeuuid,
PRIMARY KEY (id, created_at)
) WITH CLUSTERING ORDER BY (created_at DESC)
AND additional_write_policy = '99PERCENTILE'
AND bloom_filter_fp_chance = 0.01
AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
AND comment = ''
AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
AND crc_check_chance = 1.0
AND default_time_to_live = 0
AND gc_grace_seconds = 864000
AND max_index_interval = 2048
AND memtable_flush_period_in_ms = 0
AND min_index_interval = 128
AND nodesync = {'enabled': 'true', 'incremental': 'true'}
AND read_repair = 'BLOCKING'
AND speculative_retry = '99PERCENTILE';Particular column
If a column exists, a SELECT command will return any data stored in the column:
SELECT * FROM cycling.upcoming_calendar WHERE year = 2015 AND month = 6;Results
year | month | description | events
------+-------+------------------------------------------------------------------------------+----------------------------------------------------------------------------
2015 | 6 | {'Criterium du Dauphine': 'Easy race', 'Tour du Suisse': 'Hard uphill race'} | ['Tour de France', 'Criterium du Dauphine', 'Vuelta Ciclista a Venezuela']
(1 rows)
year | month | description | events
------+-------+------------------------------------------------------------------------------+----------------------------------------------------------------------------
2015 | 6 | {'Criterium du Dauphine': 'Easy race', 'Tour du Suisse': 'Hard uphill race'} | ['Tour de France', 'Criterium du Dauphine', 'Vuelta Ciclista a Venezuela']
(1 rows)
year | month | description | events
------+-------+------------------------------------------------------------------------------+----------------------------------------------------------------------------
2015 | 6 | {'Criterium du Dauphine': 'Easy race', 'Tour du Suisse': 'Hard uphill race'} | ['Tour de France', 'Criterium du Dauphine', 'Vuelta Ciclista a Venezuela']
(1 rows)See also:
